How do I avoid pitch deviation of an aircraft?

Adjust the autopilot PID

@SoulBlazer Thanks for the advice. I will post the craft so you can see what's the problem.

@SoulBlazer Right when I take off, then it stabilizes itself, but still tends to be dragged. Is it because of a weak part lift? I've seen a couple of aircraft that do not have this behavior. I changed the drag force of the wings and the deviation is reduced. Still, the velocity retrograde is not in the same direction with the set one (for example, I set the pitch to 9 and the velocity is at 2 or 3).